I. Field of the Invention
The present invention relates generally to fuel control systems for internal combustion engines and, more particularly, to a fuel control system during a cold start engine condition.
II. Description of Related Art
Most modern day internal combustion engines of the type used in automotive vehicles include a plurality of internal combustion chambers. An intake manifold has one end open through a throttle to ambient air and its other end open to the internal combustion chambers via the engine intake valves. During a warm engine condition, a multipoint fuel injector is associated with each of the internal combustion chambers and provides fuel to its associated internal combustion chamber. The activation of each multipoint fuel injector is controlled by a processing circuit or electronic control unit (ECU).
During a cold start engine condition, however, a single cold start fuel injector is oftentimes used to provide the fuel charge to several or all of the combustion chambers for the engine. The cold start fuel injector injects sufficient fuel into a cold start fuel passageway open at its outlet to the air intake passageway to provide the fuel charge to the engine during engine warm up. As the engine warms up, the cold start fuel injector is gradually deactivated while, simultaneously, the multipoint fuel injectors are gradually activated in order to provide a smooth transition between the cold start fuel injector and the multipoint fuel injectors.
These previously known fuel control systems for the engines during engine startup, however, have suffered from a number of disadvantages. One such disadvantage is that it is necessary to provide an overly rich fuel mixture to the engine during a cold start engine condition in order to ensure proper engine starting. Many of the previously known systems which have a cold start fuel injector utilize electric heaters within the cold start fuel passageway to vaporize the fuel prior to its induction into the internal combustion engine. However, because it is necessary to provide a relatively large quantity of fuel in order to obtain the overly rich combustion charge to the engine combustion chambers to ensure smooth engine starting, in many cases, the fuel injected by the cold start fuel injector overly cools the electric heater. When this happens, unvaporized fuel is inducted into the engine combustion chambers during engine startup. Such unvaporized fuel disadvantageously increases noxious emissions from the engine in excess of those required by governmental emission regulations.
A still further disadvantage of these previously known fuel management systems during engine startup is that typically the cold start fuel injector is only activated once the engine attains a certain rotational speed, e.g. 70–100 rpm. When that rotational speed is obtained, the ECU begins activation of the cold start fuel injector. However, after this rotational speed is attained during engine cranking, the internal combustion engine must induct all of the air from the cold start fuel passageway before the actual air/fuel mixture from the cold start fuel injector actually reaches the internal combustion chambers of the engine and thus before actual fuel combustion can begin. This delay is known as the cold start fuel injector transport delay. In many cases, the delay can extend as long as eight combustion cycles for the engine.
A still further disadvantage associated with the cold start fuel injector transport delay is that, when the fuel charge from the cold start fuel passageway actually reaches the engine combustion chambers, only a partial air/fuel mixture is inducted into the engine combustion chamber during the first initial intake cycles for the engine. This partial fuel charge is typically insufficient to achieve engine combustion in the combustion chamber thus resulting in an uncombusted fuel charge in the engine exhaust. Such uncombusted fuel causes unacceptable engine emissions.
Many modern engines further include a catalytic converter connected to the exhaust stream from the engine. The catalytic converter eliminates, or at least greatly reduces, noxious engine emissions in the well known manner. However, it is necessary for the catalytic converter to achieve a predetermined operating temperature before the catalytic converter effectively operates to reduce and/or eliminate noxious emissions from the engine. With the previously known fuel control systems, the actual time delay from engine combustion until the time that the catalytic converter reaches its operating temperature is prolonged and oftentimes exceeds thirty seconds or more. Until the catalytic converter reaches its operating temperature, however, it will be ineffective to reduce noxious emissions from the engine.
It has been previously known to retard the spark ignition in order to achieve more rapid heating of the catalytic converter. However, such spark retardation for all of the engine cylinders results in poor and overly rough engine start.